A Swedish research team has announced several successful pregnancies in mice that received uterus transplants. It's the first time a womb transplant has worked in any animal.

"These are the first true transplants in the world to produce live births," lead researcher Mats Brännström, MD, PhD, says in a news release. Brännström is professor of obstetrics and gynecology at Sahlgrenska University, Götenborg, Sweden.

The womb donors and recipients were genetically identical mice. After transplantation, the wombs produced offspring. All the mouse pups were healthy, fertile, and seemed normal, the researchers announced at this week's meeting of the European Society of Human Reproduction and Embryology.

Brännström's team also looked at how long a donated uterus could be preserved before transplant.

"In mice, at least, the time limit for removing a uterus and transplanting it is between 24 and 48 hours," Brännström says.

Experiments with unrelated mice showed that the recipient's body rejects wombs from unrelated donors. Immune suppressing drugs would have to be used to prevent rejection. It's not clear what effect these potent drugs would have on a developing fetus.

The Swedish team is now experimenting with womb transplants in pigs. They hope to perfect the technique for humans. Brännström says 3%-4% of infertile women might benefit from womb transplant.

"This includes women with congenital malformations, those born without a uterus, and those whose uterus is defective," he suggests. "It may also benefit women who have lost their uterus because of emergency operations due to post-partum hemorrhage, and those who have had early stage cervical cancer."